The best time to buy bitcoin, if they have more bitcoin in your wallet then if they see the price is high then no more doubts to buy for it.
If you are sure and have your feelings or analysis is correct then do it. I'm also sure if this is the right time to buy more bitcoins. A few weeks this bitcoin price does not fall below $ 7k so there is a possibility the bitcoin price will rise gradually.
In my opinion it is a matter of money. When you have money you will not look the price. I noticed that when the price was about $4000 many people said that now it is not good to invest in bitcoin because the price is too high and it will not grow more but we saw that in just few months it reached to $20000 and the investors made thousands of dollars.